Introduction
Swell and shrink questions come up on nearly every excavation job: what the factors mean, which one to use, how bank, loose, and compacted yards relate, and how the numbers turn into trucks and budgets. The Spoil Swell Calculator runs the conversions — bank to loose through the swell factor, loose to compacted through the shrink factor, plus unit conversion and truckload counts. The answers below explain the thinking behind each output. For the full method with a worked example, see the complete guide.
Frequently Asked Questions
What is the difference between bank, loose, and compacted cubic yards?
Bank cubic yards (BCY) measure soil in place, before excavation — the volume the hole will be. Loose cubic yards (LCY) measure the same soil after excavation, when it has fluffed up with extra air voids; LCY is always larger than BCY. Compacted cubic yards (CCY) measure soil after placement and compaction — denser than loose, usually close to but rarely exactly bank. Trucks, dump fees, and stockpiles work in loose yards; excavation plans work in bank yards; finished grades work in compacted yards.
What is the formula for spoil swell?
Loose = Bank × (1 + Swell factor). A 100-BCY cut of common earth at 25% swell becomes 100 × 1.25 = 125 LCY. The reverse conversion for fill is Compacted ≈ Loose ÷ (1 + Shrink factor). The formula guide derives both from the definition of the factors.
What swell factor should I use for my soil?
Use these typical planning ranges, remembering that site conditions vary: topsoil 10–15%, sand and gravel 10–15%, common earth 20–25%, clay 25–35%, rock 40–60%. Wet conditions push toward the high end; confirm against local experience or geotechnical data for structural work. The material guide details how each soil behaves.
How many truckloads will my excavation need?
Divide the loose volume by the truck’s loose capacity and round up: Loads = LCY ÷ truck capacity. Example: 100 BCY of common earth at 25% swell = 125 LCY; with 12-yd³ tri-axles that’s 125 ÷ 12 = 10.42 → 11 loads. Quoting on bank yards instead of loose is the most common estimating error — it undercounts loads by exactly the swell percentage.
How much does 100 bank cubic yards swell to in metric?
100 BCY × 0.7645549 = 76.5 m³ in place. At 25% swell: 76.5 × 1.25 = 95.6 m³ loose. (Check: 125 LCY × 0.7645549 = 95.57 m³ — the systems agree.) Remember 1 m³ = 1.308 yd³ for converting the other direction.
Why does ordered fill come up short of the hole?
Because fill is delivered loose and only shrinks after compaction. A 100-compacted-yard backfill at 25% shrink needs 100 × 1.25 = 125 loose yards delivered. Ordering 100 yards “to match the hole” leaves the grade short by the shrink percentage. Always order fill in loose yards.
Are swell and shrink factors the same number?
Approximately, for planning. Excavation method sets the swell (blasting loosens more than careful digging) while compaction effort sets the shrink (a sheepsfoot roller achieves more than a plate compactor), so the two can differ on a real job. Using matched factors is a reasonable planning approximation; confirm both against actual methods for anything structural.
How do I estimate a cut through two different soils?
Split the bank volume by layer, apply each layer’s factor separately, and add the loose volumes. Example: 40 BCY of topsoil at 12% (44.8 LCY) plus 60 BCY of clay at 30% (78 LCY) = 122.8 LCY total. A single blended factor underestimates the harder layer.
What size truck should I assume for haul-off?
A tri-axle dump truck typically carries 10–15 yd³ loose per load. Always confirm the carrier’s actual loose capacity — and whether your material will be volume-limited or weight-limited (wet, dense soils hit legal weight before the bed fills). For budgeting hauling, see the cost guide.
Does the calculator account for moisture?
The calculator applies the factor you enter — it can’t see your site. Wet soil swells more (and weighs more per load) than the same soil dry. After sustained rain, use the high end of the soil’s range, and discuss weight limits with your hauler. The pro tips cover moisture adjustments.
How accurate are these conversions?
They’re planning estimates, not lab measurements. The arithmetic is exact; the uncertainty lives in the inputs — the soil identification, the factor, the bank measurement, and the moisture. Good practice: anchor against the 100-BCY reference (100 bank yards of common earth at 25% swell = 125 loose yards ≈ 11 tri-axle loads), cross-check metric against imperial, and re-run when conditions change.
Can I reuse excavated spoil as backfill?
Often, with caveats. Suitable granular or common-earth spoil compacts well and saves both a haul-off load and a fill purchase. Organic topsoil, wet clay, and debris-laden material usually don’t qualify as structural backfill. Check the material guide for suitability, and confirm compaction requirements with the project specs — some fills require tested density, not just arithmetic.
Related Guides
- Spoil Swell Calculator: Complete Guide — the full method with a worked example.
- Spoil Swell Calculator: Formula Explained — derivations of the swell and shrink formulas.
- Spoil Swell Calculator: Material Guide — soil types and their swell behavior.
- Spoil Swell Calculator: Cost Guide — hauling and tipping budgets from loose yards.
- Spoil Swell Calculator: Estimating Guide — the takeoff workflow behind the numbers.
Get Your Number
If your question isn’t answered above, the fastest path is to run your own numbers: enter the bank volume and your soil’s factor into the Spoil Swell Calculator, then check the loose-yard and load-count outputs against the formulas and examples on this page. When the arithmetic and the intuition agree, the number is ready to quote against.
Disclaimer: Calculator results and the figures on this page are planning estimates. Actual swell and shrink vary with soil type, moisture, excavation method, and compaction effort. Verify quantities against site conditions and consult a licensed professional or your local authority for structural, environmental, or code-related decisions.
1 comment